This invention relates to a lysimeter probe that is a device used for measuring percolation of water through soils and sampling soil water for chemical analyses. A lysimeter is generally a tank or container inserted into the soil used to define the water movement across a soil boundary. The lysimeter of the present invention is especially designed for golf course groundwater monitoring; it monitors chemicals and groundwater recharge transmission to and in the groundwater.
A typical design consists of a porous cup attached to a PVC sample accumulation chamber and two access taps that lead to the soil surface.
Lysimeters have been used for over 300 years to determine water use by vegetation. Precision lysimetry for measuring evapotranspiration (ET) has developed mainly within the past 50 years. Weighing lysimeter designs are quite varied to suit individual research requirements. Surface areas from 1.0 meters to over 29 meters have been used. ET accuracy depends directly on the lysimeter area, mass, and the type of scale, but many lysimeters have accuracies better than 0.05 millimeters. Few weighing lysimeters exceed 2.5 meters profile depth. Mechanical, floating, hydraulic, and electronic scales have been used in weighing lysimeters with varying types of data recording methods. Lysimeter wall construction can affect heat transfer to the lysimeter and water flow along the walls. ET accuracy of weighing lysimeters can be affected by many additional factors (personnel traffic, cultural operations, crop height, etc.).
Lysimeters have become standard tools in evapotranspiration (ET) and water quality research. An excellent review of the history of evaporation research and experimental methods is found in Brutsaert (1982). Historical accounts of ET research, in particular lysimeter developments, are found in Kohnke et al. (1982). Soileau and Hauck (1987) reviewed lysimetry research with an emphasis on percolate water quality, and Bergstrom (1990) discussed lysimetry applications for pesticide leaching research.
Lysimeter is defined in Webster's New Collegiate Dictionary as a "device for measuring the percolation of water through soils and for determining the soluble constituent removed in the drainage". The word "lysimeter" is derived from the Greek words lysis which means dissolution or movement, and metron which means to measure. Clearly, the word lysimeter means the measurement of the percolation of water in soil, although other devices to remove water samples from soil are called "lysimeters". The water use (evaporation, transpiration, or ET) can be determined by a balance of the water above this boundary. Weighing lysimeters determine ET directly by the mass balance of the water, as contrasted to non-weighing lysimeters which indirectly determine ET by volume balance.
The first lysimeter for the study of water use has been attributed to De la Hire of France in the late 17th century. A lysimeter study was conducted in the Netherlands in early 17th century, probably about 1620, by Van Helmont. Principle advances in ET lysimetry have centered on the measurement of the lysimeter mass and vacuum drainage and deeper lysimeters to more closely duplicate field conditions. The weighing mechanisms--mechanical, floating, hydraulic, or electronic--can be automated for electronic data recording. Major advances have occurred in the past 20 years in recording weighing lysimeter data.
Lysimeter designs have been copied or duplicated. However, Kohnke et al. (1940) cautioned "that no one construction should be regarded as standard in a lysimeter and that a proper design can be made only by having an accurate knowledge of both the purpose of the experiment and of the pedologic, geologic, and climatic conditions". Pruitt and Lourence (1985) cautioned each lysimeter user to critically evaluate all agronomic aspects to ensure the representative high quality ET data since major errors in ET data are possible even with an accurate lysimeter.
In ET research, lysimeters are simply containers or tanks filled with soil in which plants are grown. Lysimeters have been classified according to type of soil block used, surface drainage, and methods of measuring soil water content. The method of drainage may be gravity or vacuum, or a water table may be maintained. Lysimeters for ET research are usually classified as monolithic or reconstructed soil profiles, as weighing or non-weighing, and as gravity or vacuum drainage.
Water percolating from the surface to the groundwater aquifer can carry pollutants in solution which may ultimately contaminate drinking water wells. In many instances, wells used to extract drinking water have been contaminated by agricultural chemicals and other pesticides used at the surface. Percolation takes a long time. Once aquifers are contaminated, cleaning them is a long term, expensive process. Early indications of potential contaminants can be obtained by sampling water from the soil a few feet below ground level before water reaches saturated levels. Lysimeters are used to sample water from the unsaturated vadose zone. The water pressure in the vadose zone is below atmospheric due to capillary effects. The suction effect produced by capillarity has to be overcome for successful water sampling from this zone. Lysimeters have mechanisms to achieve this for successful operation.
A need exists for a compact lysimeter which is accurate and easy to install and use. Additionally, a need exists for accurately collecting and measuring water moving through the vadose zone whereby a sample is suitable for trace containment analysis.
Golf courses and other operations that use chemicals need to sample concentrations of chemicals moving through the vadose zone. Currently a lysimeter device is not available to perform this type of measurement.